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Commit 67c6777a authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds
Browse files

binfmt_elf: safely increment argv pointers 

When building the argv/envp pointers, the envp is needlessly
pre-incremented instead of just continuing after the argv pointers are
finished.  In some (likely impossible) race where the strings could be
changed from userspace between copy_strings() and here, it might be
possible to confuse the envp position.  Instead, just use sp like
everything else.

Link: http://lkml.kernel.org/r/20170622173838.GA43308@beast


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Qualys Security Advisory <qsa@qualys.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a73dc537

fs/binfmt_elf.c

+9 −11
Original line number Diff line number Diff line
@@ -163,8 +163,6 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, 
	unsigned long p = bprm->p;

	int argc = bprm->argc;

	int envc = bprm->envc;

	elf_addr_t __user *argv;

	elf_addr_t __user *envp;

	elf_addr_t __user *sp;

	elf_addr_t __user *u_platform;

	elf_addr_t __user *u_base_platform;
@@ -304,38 +302,38 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, 
	/* Now, let's put argc (and argv, envp if appropriate) on the stack */

	if (__put_user(argc, sp++))

		return -EFAULT;

	argv = sp;

	envp = argv + argc + 1;



	/* Populate argv and envp */

	/* Populate list of argv pointers back to argv strings. */

	p = current->mm->arg_end = current->mm->arg_start;

	while (argc-- > 0) {

		size_t len;

		if (__put_user((elf_addr_t)p, argv++))

		if (__put_user((elf_addr_t)p, sp++))

			return -EFAULT;

		len = strnlen_user((void __user *)p, MAX_ARG_STRLEN);

		if (!len || len > MAX_ARG_STRLEN)

			return -EINVAL;

		p += len;

	}

	if (__put_user(0, argv))

	if (__put_user(0, sp++))

		return -EFAULT;

	current->mm->arg_end = current->mm->env_start = p;

	current->mm->arg_end = p;



	/* Populate list of envp pointers back to envp strings. */

	current->mm->env_end = current->mm->env_start = p;

	while (envc-- > 0) {

		size_t len;

		if (__put_user((elf_addr_t)p, envp++))

		if (__put_user((elf_addr_t)p, sp++))

			return -EFAULT;

		len = strnlen_user((void __user *)p, MAX_ARG_STRLEN);

		if (!len || len > MAX_ARG_STRLEN)

			return -EINVAL;

		p += len;

	}

	if (__put_user(0, envp))

	if (__put_user(0, sp++))

		return -EFAULT;

	current->mm->env_end = p;



	/* Put the elf_info on the stack in the right place.  */

	sp = (elf_addr_t __user *)envp + 1;

	if (copy_to_user(sp, elf_info, ei_index * sizeof(elf_addr_t)))

		return -EFAULT;

	return 0;